The present invention relates generally to the field of semiconductor wafer lithography, and more particularly to optimizing shutter arrangement in lithography steppers.
Lithography systems for lithography processing generally involve tools and processes to expose a desired pattern onto a resist layer on a semiconductor wafer, to develop the resist layer, and to remove the portions of the resist exposed (or, not exposed depending on the resist type). Then, following the lithography processes, further processing of the semiconductor wafer occurs, for example, by etching the underlying layer, implanting elements or depositing additional material using the developed resist layer. The processes to expose a pattern on a resist layer are commonly performed using a step and scan exposure tool such as a lithography stepper. A lithography stepper generally exposes a reticle field by scanning a slit of fixed width from one end of the reticle field to the other or, in some cases, by keeping the slit fixed and moving the wafer. A reticle is another name used for a lithography mask created from semiconductor design data such as semiconductor chip design data or semiconductor wafer data. Lithography imaging is highly dependent on wafer surface uniformity and circuit design elements to be processed, such as component patterns, line density, circuit devices or elements (i.e. microprocessor, cache, or deep trench capacitors).
Integrated circuits used in semiconductor chips are usually composed of distinct circuit components. Semiconductor chip components such as microprocessor cores, cache, and accelerators may be repeated on a semiconductor chip numerous times. The components such as microprocessor cores, accelerators, and cache typically have different design styles resulting in different types of patterns or metal patterns for designing components. Each type of component may have different parameters such as average metal density in the back end of the line (BEOL). Significant differences in average metal density can occur when one component has a much higher metal density than another nearby component, and can lead to differences in optimal processing conditions such as focus, dose, or ultraviolet light source used in lithography systems for the various components.